High friction plastic conveyor belts having modular links formed by two integrated plastic materials

Abstract: A plastic conveyor belt system provides high frictional surface contact between the conveyor work surface and the load carried by the conveyor. This is achieved by modular belt links integrally formed of two diverse plastic materials such as a low friction polypropylene and a high friction elastomer thermoplastic rubber. Typically a belt modular link having a planar load support area 12 disposed in its lower forming mold piece 21 with an upper mold piece 22 removed to expose the planar area 12. Then a further mold piece 23 is mated with the lower mold piece 21 to integrally join by thermal bonding the two diverse materials producing on the planar link load bearing surface area an elastomer strip 16, 19 with an outer patterned surface for encountering the belt load. The modular belt links are coupled in a belt array to dispose paths 40, 42 along the length of the belt upper and lower surfaces where a belt supporting member 31, 33, 45, 46 frictionally encounters the low friction plastic material.

Description: TECHNICAL FIELD: This invention relates to plastic modular conveyor belts and more particularly it relates to conveyor belts with plastic modular links integrally formed of two different plastic or rubber materials. BACKGROUND ART: Modular plastic links for conveyors are typically formed of polyethylene, polypropylene or acetal, which are hard, wear resistant plastics having a low coefficient of friction ideal for pivoting the links and frictional contact with wear strip surfaces. These plastics also provide a high tensile strength along the belt for conveying heavy loads and ideal chemical and biological inactivity for use of the belts in sanitary and chemical environments. However, the low friction characteristics of the plastics do not form an ideal belt-to-load surface for carrying loads up and down inclines. EP-A-0 523 810 discloses a conveyor link module showing practically most of the features recited in the head clause of claim 1 of the present patent and particularly disclosing the idea of affixing a resilient pad to the link module by thermal bonding in order to form an integral body. The resilient material and the low friction material being incompatible for direct bonding, the use of an intermediary frame for affixing the two pieces together has been proposed. It is a primary object of this invention to provide a less complicated to manufacture high friction link belt module. DISCLOSURE OF THE INVENTION: In accordance with this invention modular plastic link belts are formed by a plurality of individual links pivotably coupled end-to-end by pivot rods passed through interdigitated link end fingers, each link comprising the features as defined in claim 1. Further objects, features and advantages of the invention will be found throughout the following description, drawings and claims. BRIEF DESCRIPTION OF THE DRAWINGS: In the accompanying drawings, wherein like reference characters refer to similar features throughout the various views to facilitate comparison: Figure 1 is an exploded perspective sketch of a modular belt link afforded by this invention having an integral body formed of two different materials, respectively characterized by low and high coeffidents of friction; Figure 2 is a plan view of a high friction textured overlay pattern for forming a load carrying surface of a conveyor belt; Figures 3 to 5 are respectively section sketches of a lower and two alternating upper mold pieces employed to integrally mold a modular belt link from two different materials in accordance with this invention; Figure 6 is a side view sketch, partly in section. showing a fragment of a modular link belt with modular links pivoted together; Figure 7 is a fragmentary side view sketch of a sprocket driven conveyor belt system embodying the invention; Figure 8 is a cross-sectional elevational view of a conveyor embodying the invention showing an upper carryway and a lower retumway with the belt supported by wear strips in contact with low friction surface portions; Figure 9 is a perspective fragmental view of a high friction layer having a bed of teeth pointed outwardly from a belt surface to receive and resiliently conform with the shape of an object being transported on the belt; Figure 10 is a plan view of the load bearing surface on a length of conveyor belt constructed of bricklayered links formed with an integral surface layer of soft rubber-like resilient plastic material bonded on the load bearing surfaces of hard plastic links; and Figure 11 is a perspective end view of a belt fragment of Fig. 10 showing the high friction surface material pattern with a gap between interdigitated appendages to permit a degree of backward articulation of the belt. THE PREFERRED EMBODIMENTS: The modular link of Figure 1 has the anti-skid conveyor load carrying surface member 11 and the link end carrying base member 12 formed of two separate materials bonded together integrally at the top surface interface 15. The base element 12 is formed of a strong, hard plastic material having a low coefficient of friction, typically acetal, polypropylene or polyethylene, and the surface member 11 is of an elastomer, typically a thermoplastic rubber having a high coefficient of friction. The elements are bonded together at the interface surface 15 by thermal injection molding. The surface friction member 11 in one embodiment is textured to present an anti-slip high friction load carrying surface having diamond shaped ridges 16 extending upwardly from an unapertured carrying surface strip 17. When the friction member 11 is superimposed on the flat-top surface 15 of the base elements 12 connected pivotably end to end, there will be a gap between the strips 17 extending over the link ends 18 of the base elements 12. However, the textured surface of the modified friction member 11' in Figure 2 provides mating link end members 19 that will overlap and interdigitate with the link ends 18 to form a substantially continuous load bearing anti-slip surface over the length of the belt. It should be appreciated that, although the embodiments shown have flat-top surfaces, it is also possible to have perforated or otherwise open-area belt modules for drainage or air flow. The integral modular links are molded in the manner represented by the mold pieces shown in Figures 3, 4 and 5. Thus the base member 12 resides in the lower mold half 21 after the upper die half 22 has been removed. Then the alternating die half 23 is mated with lower die 21 to thermally bond the surface member 11 to the flat upper surface of link 12, by injection molding. Belt systems constructed with interconnected finished modular links 25, 26, as shown in Figure 6, representing a fragmental portion of a pivoted link conveyor belt 24 in Figure 7, thus present an anti-slip upper load bearing transport surface 27 formed of the high friction material, and a lower link base of stronger and longer wearing hard plastic having lower friction. The low friction material of the base member 12 at the pivot zones 29 is crucial, as is the low friction interface at the wear plates 31 of the conveyor belt array of Figure 7. Also the low friction interface of the sprocket teeth 32 with the hard plastic low friction material is crucial to belt wear and permits the use of more positive sprocket drive to replace rollers that were used heretofore with fabric belts necessary to provide high friction load carrying interfaces. Since the softer resilient elastomeric material of the anti-slip surface 27 is more subject to wear, the lowermost return path of the link belt is passed over small diameter rollers 33 in embodiments where there must be contact with the high friction material. The resulting conveyor link belt system is not compromised in terms of pulling capacity or tensile strength with the construction of links as taught by this invention. Another advantage of the modularity of the invention is that various patterns of high-friction surfaces can be arranged in constructing a conveyor belt For example, as shown in Figure 8, belt modules 40 lacking high-friction conveying surfaces can be bricklayed with modules 41 having high-friction surfaces in a load-bearing surface pattern characterized by low-friction bands 42 along the edges 43 or internal portions 44 of the belt. Stationary wearstrips 45 or shoes 46, rather than the moving roller 33 of Figure 7, can be positioned along the return path 47 in line with the low-friction bands 42 to minimize friction and wear. Equivalently, modules can be molded with longitudinal gaps between high-friction surface material so that a conveyor belt having low-friction longitudinal bands along the load-beating side can be assembled. The design of proper link belts is facilitated by the link construction, and the hard plastic is not subject to any extensive stretching or fatigue. it is noted that with the shown construction the high friction material is not required to bend as it articulates about the sprocket assembly 36 of Figure 7. This invention therefore provides in one embodiment a modular link for a plastic conveyor belt adapted to convey loads up and down inclined surfaces by way of a thermally bonded surface member 11 affixed unitarily to a basic modular link to serve as a high friction load transport body. Thus, surface member 11 is made of high friction elastomeric material that thermally bonds to form a unitary modular link with the basic plastic modular link body of base member 12. Thus a basic modular link formed of hard, wear resistant plastic material having a low coefficient of friction with a shape presenting a load carrying surface with a substantially planar load bearing area 15 is converted into a high friction modular link capable of carrying loads up and down an inclined surface. The hard plastic region serving as interface surface 15 forms a thermal bond with dissimilar compressible thermoplastic frictional materials to produce a unitary modular conveyor belt link of different load bearing characteristics. These links when coupled end-to-end form a belt of predeterminable fixed length that retains high longitudinal belt strength and low friction contact surfaces for belt transport bearing surfaces and pivot joints. Improved conveyor belt systems using these modules function over a wide range of loading requirements including transport up and down inclined surfaces. The high friction load transport body encompasses substantially the entire load bearing area of the modular links to produce maximum load support, friction and bonding strength. A textured surface (Figs. 1,2) extending outwardly from the surface of the high friction material in a set of interconnected ridges will conform resiliently to load bodies in contact therewith for additional functional advantage in conveying different types of loads. The load transport body in the embodiment of Figure 2 has interdigitatable link end fingers extending from the main body of high friction material to overlap the link end fingers 18 on the basic module (Fig. 1). The high friction material does not interfere with the favorable drive characteristics of the low friction hard plastic of the basic modular link structure, and therefore serves advantageously with sprocket drive gear transport of the belt That is, there is no particular forces on the large thermoplastic bonded area that tends to disrupt the unity of the load bearing modular unit, since the load offers basically a downward compression with little shear force that would tend to cause catastrophic failure. Furthermore, the placement of the two diverse materials in the modular link conveyor belts of this invention is such that the hard plastic material is used to contact frictionally wear strips with minimal friction. In particular, this invention provides two compatible modular links which may be bricklayed in a conveyor belt of desired width to provide separate lanes of either modules with high friction load bearing surfaces to transport loads or with low friction long lasting plastic surfaces that mate with wear strips, typically installed on belt return paths, which would otherwise interfere with high friction surfaces on the load bearing surfaces unitary modules formed from diverse materials supplied by this invention. The Figure 9 embodiment of the surface layer 50 to be bonded upon the hard plastic link load bearing surface has a bed of teeth 51 extending vertically outwardly from the belt surface. The individual teeth in the bed 51, for example, one-quarter inch long and the tooth density is about forty per square inch. This constitutes an ideal surface configuration for transporting fruit such as peaches when supplied with very soft resilient teeth that are not stiff enough to penetrate or damage the fruit The belt configuration of Figures 10 and 11 shows the bricklayering of seven links 53, 54, etc. separated at seams 56 to form a predetermined belt width wider than a single link. The bonded integral high friction layers have a horizontally disposed tooth pattern 58 with individual teeth 59 extending over the link ends 60 in a zig-zag pattern that simulates saw teeth, for example. The teeth 59 on adjacent end-to-end pivotably connected links are interdigitated and preferably overlap to form substantially a continuous end-to-end frictional surface along the length of the belt There is purposely left a gap 61 between the surface layers on two end-to-end connected links of a horizontally extending belt surface in order to permit more freedom of articulation of the links in the belt path about the pivot axes 65. Thus, as seen in Figure 11, there is a limited degree of backward articulation over the angle Ø permitted before the teeth 59 abut the notches 66 of this rectangular sawtooth surface pattern of surface layer 55. Thus the toothed appendages 59 and accompanying notches 66 form a substantially rectangular zig-zag pattern substantially parallel to a pivot axis through the fink ends. This is necessary to permit the belt to react without binding under conditions for example encountered as it backflexes on its approach to support surfaces on the returnway path. There is provided in this embodiment, as shown in Fig. 10, a longitudinally disposed lane 70 devoid of the surface layer 55 which permits the use of a wearplate or similar function support member for the belt riding In frictional contact with the hard plastic low friction link surfaces shown at the right end of the belt. However for the rest of the belt width, the load bearing surface of the belt which is co-planar with the aperture carrying link ends is substantially fully covered by the soft resilient high-friction material, and thus overlaps a significant part of the interdigitated link end fingers 60 on ajacent end-to-end links extending from and coplanar with the load bearing surface.

Claims: A modular link for a conveyor belt formed of a plurality of the modular links pivotably coupled end-to-end by pivot rods passed through interdigitated link end fingers (18), said link being formed of a hard plastic material base element (12) having a low coefficient of friction and presenting a rigid high strength flat load conveying surface (15) for the conveyor belt and carrying a high friction resilient surface material (11) in contact therewith to outwardly extend from said load conveying surface (15) of said hard plastic material over a substantial portion of the flat load conveying surfaces (15, 50) thereby forming an integral body (53, 54, etc.) therewith, said surface material (11) presenting a patterned surface having a resiliency that gives with the weight of load bodies in contact therewith being conveyed by said belt, said surface material (11) being a soft thermoplastic rubber like material thermally bonded over its entire contact surface with the hard plastic material (12) onto the hard plastic material (12) by thermal injection molding (21, 22, 23). The link of Claim 1 further characterized by a load carrying surface substantially disposed in a plane and comprising co-planar sets of said link end fingers (18) extending from respective ends and having a set of pivot rod receiving apertures axially aligned therein and disposed between two substantially parallel link sides, wherein said resilient surface material has fingers (19, 60) extending onto said link end fingers (18, 59). A modular plastic conveyor belt formed of a plurality of modular links (25, 26, 40, etc.) according to claim 1 or claim 2, connected end to end. The belt of Claim 3 having two outer substantially parallel edges (43) further characterized by : a substantially planar surface (42, 44, 70) along the length of the belt load carrying surface partially devoid of said high friction material (11). The belt of Claim 3 further characterized by : a low-triction belt-supporting load-bearing wear strip surface (45) positioned at an outer edge of the belt in low friction sliding frictional engagement with hard plastic low friction outer belt edge surfaces (42) of the link bodies moving along the conveyor belt path. The conveyor belt of Claim 3 further characterized by : said modular links having extended ridges of the hard plastic low friction material defining sprocket drive means for contact with a sprocket drive gear to the exclusion of contact with the high friction material. The conveyor belt of Claim 3 further characterized by : a substantially continuous aperture free outer surface pattern of the high-friction surface material (11,27,41,55) disposed to produce a substantially continuous constant width load bearing conveying surface along the belt The conveyor belt of Claim 3 further characterized by : a region devoid of the high resistance surface layer comprising at least one longitudinally disposed lane (42, 44, 70) along said conveyor belt consisting of low friction plastic link body surfaces, whereby the belt presents an outer belt surface load bearing area with a low friction surface (27, 41, 55). The conveyor belt of Claim 3 further characterized by : a plurality of modular links (53, 54, etc.) bricklayed into a belt configuration of predetermined width with said high friction material (11, 55) substantially covering the width of the belt The belt of Claim 3 comprising at least some regions (42, 44, 61) on the load carrying surfaces of the links devoid of the high friction surface material (11,27,41,55). The link of Claim 1 further characterized by a patterned surface (16) comprising ridges outwardly extending from a substantially planar base (15) of the high friction material (11). The link of Claim 1 further characterized by a patterned surface comprising a plurality of tooth-like appendages (51) extending from a substantially planar load bearing surface (15). The link of Claim 12 wherein said rubber like material (11) comprises horizontal extensions (19) from the load bearing surface toward the link end fingers (18) to produce saw-tooth like leading and trailing edges. The link of Claim 13 wherein said extensions (19) overlap onto the link end fingers (59). The link of Claim 14 wherein the extensions (19) of high friction material (11, 27, 55) are dimensioned to produce for adjacent end-to-end coupled links a gap (61) between mated teeth (59) and notches (60) that permit a limited degree of backward articulation of links toward the load bearing surface by resilient abutment of the surface material (11, 27, 55) on two adjacent links. The link on Claim 13 wherein said extansions (19) form a substantially rectangular zig-zag pattern (58) substantially parallel to a pivot axis through the link ends. The link of Claim 1 wherein teeth (51) extend vertically from the load bearing surface (15). The link of Claim 17 wherein said teeth (51) comprise a bed of closely spaced teeth extending outwardly at least one-quarter inch and wherein said outer surface material (50) is soft enough to bend and provide a nest in the presence of small sized fragile load objects such as fruits without penetration and damage.

Inventors: CARBONE JOHN J, LAPEYRE ROBERT S, CARBONE, JOHN J., LAPEYRE, ROBERT S.
Applicants: LAITRAM LLC, LAITRAM L.L.C.
Application year: 1994
Main classification: B65G17
IPC codes: B65G17, B65G15